Hearth type furnace



July 7, 1953 H. w. BEECHER 2,644,431

. HEARTH TYPE FURNACE Filed Aug. 29, 1949 4 sheets-sheet 1 :inventor July 7, 1953 H. w. BEI-:CHER

HEARTH TYPE FURNACE 4 Sheets-Sheet 3 Filed Aug. 29, 1949 @Gigli N HENRY M/ 5556/15@ Gtorneg H. W. BEECHER HEARTH TYPE FURNACE July 7, 1953y 4 sheets-sheet 4 Filed' Aug. 29, 1949 Gttorneg Patented July 7, 1953 HEARTI-I .TYPE FURNACE Henry W. Beecher, Seattle, Washi; Blanche Cameron. Beecher and Henry Ward Beecher, Jr., executors of said Henry W. Beecher, deceased Application August 29, 1949, Serial No. 1 12,907

Iohis inventionfrelatesto furnaces, and more particularly to hearth-type furnaces vdesigned for use `in burning wood or similarvk fuels under water tube boilers. v

v.'Ifo burn woodwaste fuel efcientlyin a furnace, the followingl conditions shouldbe provided to furnace temperatures in order to effect evaperationvr o f moisture in the fuel and the distillation of volatiles.

' ,Seconde.-Fresh fuel 'should progressively enter-r thejfurnace'inf'such a manner 4that it does not coverthey fuel previously fed thereto,aand the fuel bed. should movegradually from a zone of distillation into a zone in which onlythe fixed carbon` remains. 'IhereshOuId be a minimum overlaying of wet fuel. 1 `v'Ihird- Pre-heated'y air through the green fuel t o drive off volatiles and .moisturepand additional pre-heated'Vr air should pass through the zone offincandescent carbon lat lsuch a ratethat amixture of carbon monoxide and carbon dioxide is formed; the former being Vconverted to carbon dioxide in the presence of overdraft airf Fourth-overdraft tok create 1 turbulence`v and intimate -mixing with provide a'furnace,

ing cellulose products of high moisture content, for` example,` chopped up wood waste frequently referred to as hogged fuel, with or without the aid vof supplemental fuel, and bymy improvements, to effecttheburningof the fuel in' such a' Way as to stimulate the distillation processby;

which moisture is evaporated therefrom Yand the hydro-carbon gassesy are driven off and burned in gaseousform;

It isfalso an object of my invention-to provide a furnace with a sloping, watercooled hearth or grate, comprising tubes through which a portion ofthe boiler water isfcirculated'v the tubesfbeing so disposed as to provide-restricted pass-ages f between them 'for the flowjof pre-'heated forceddraft airthrough the-fuel bed. Y j 5 A-furth'er 'object of my invention is'to` obtain better burning conditions and to insure the progression of the fuel V"bed downward along the hearth;VV This is accomplished by -dividing 'they heartharea fintofa pluralitylof zones with controlled admission of pre-heated, forced-draft .ai

to the fuelbed over each of the zones.-

air should beso rapplied as complying with the above conf ditions'for theburningof normally slow burn--A 4 claims.Y (c1. 122-2).

irst-Alarge areaof fuel should be exposed v' should be forced of air with combustible gases.

A stillfurther fobject of my invention is toV provide a furnace hearth of the above character. having sufficient area that the upper end :zone

thereof can advantageously be left partiallyor entirely uncovered by the fuel'bed, for the introduction therethrough'of pre-heated forced-draft air,A in regulated amount, to supplement airintroduced through other'overdraft 'air openings. Its admittance in this way and at this nlocation creates-greater turbulence and a better mixing Another vobject Iof my invention is to provide a hearth furnace embodying the novel features y above mentioned,A and' also including means. for.

so `maintaining and burning the` f-uel bedlthat it will gradually progress downward from the fuel inlet and avoid the overlaying of .incandescent carbon by entering fuel' andavoid-the disad.

vantages that are incident to such overlaying. It is important in a furnace that'excess air be.

kept to a minimum in order to securemaximum Y efficiency.A It is also important, for like reason,

to insure that as large a percentage as. possible.

ofthe air entering the furnace be pre-heated. Therefore, it has-been an object of this invention vto'provide means for the feeding of fuel to ther hearth through Va fuel seal that limits the cold air Yadmitted with the fuelL and prevents injecting cold'air into the furnace through the feeding opening. f

` A Further Aobjects and advantages' of the inven- 1 ltion reside in the improved-details. of construction ofthe-discharge end portion of the hearth that prevents Aadherence of slag', vand in the pro-r vision of jets forthedelivery of pre-heated air:

tothe[toe -of Vthe fuelv bed to insure the most complte burning. f

VStill further objects of my inventionfresidein the details of construction andrel'ationship of the various parts as used in the preferred and ini-the `alternative Yforms -of-construction, hereafter described.

In accomplishing the'objects of my invention, I'have provided the improveddetails of construction, the preferred forms of ywhich are illustrated inthe accompanying drawings, wherein- Fig. l is a cross-sectional view ofa-portion of avfurnace embodying'j the improvements of the present invention. f -lv -Figs.` 2 and Vv are sectional details showing alternative constructions at the lower end por- -tio-n ofthe hearth. l

Fig. '4 'is a horizontal section, taken substan-4 Fig. is an enlarged, sectional view taken on line 5 5 in Fig. 4, showing a part of the hearth and one of the zone forming plenum chambers for application of pre-heated, forced-draft air to that zone of the hearth.

Fig. 6 is an enlarged, cross-section taken on line 6 6 in Fig. 5, showing the close spacing of hearth tubes.

Fig. '7 is a detail in perspective, illustrating an alternative hearth construction.

Fig. 8 is detail in perspective of yet another.

alternative hearth construction.

Fig. 9 is a cross-sectional View of a'portion of a furnace, showing an alternative .fuel feeding system. f

Fig. 10 is a sectional detail showing an alternative construction of that portion of the furnace above the lower end portion of thev hearth.

Fig. l1 is a cross-sectional detail showing a hearth with side wall tubes.

Fig. 12 is a vertical sectional view illustrating still..another'modification of my furnace oo nstruction.

. Referring more in detail to the drawings:

In.Fig..1, wherein I have shown one form of hearth furnace and boiler system embodyingthe principal novel features of the present invention, 5 designates thefurnace chamber and 6 the combust-ionr chamber located above and in direct open communication withV the furnace chamber. the back of the furnace, is a lower masonry Wall section I and an upwardly continuing but somewhat forwardly oiset upper wall section 1m. At the front of the furnace, is a lower, vertical masonry wall section 8 of less height than section 1, and an upwardly continuing and forwardly sloping wall structure 8a3. Between the rather closely relatedwall sections l and 8 is a chamber 9, which receives the ashes andnon-combustibles from the lower end'of the hearth as presently explained.

The hearth, which is designated in its entirety by reference character l-I, comprises an inclined bank of water-tubes disposed immediately above and .supported in part by the inclined wall section 8m." The water-tubes l0, which makeup the hearth, are assembled in the same plane,in parallel relationship and closely spaced, as best shown in Figs. '4 and 6. At their upper and lower ends, respectively, the tubes are connected in the boiler circulating system by means of the hearth feeder tubes I3and riser tubes I4. n s

It is anticipated, in furnaces where-the con struction permits, or where it is advisable, that the hearth shall include at each of its opposite longitudinal edges,'a plurality of 'vertically spaced water-tubes l0' in accordance with the showing in Figs. 11 and 12. These tubes are'connected at their opposite ends with the boiler circulation preferably by connections with the headers Il and I2. Their particular purpose is to prevent the adherence of slag t0 the side Walls of the furnace, and also to absorb heat in the fuel bed along the sides of the hearth. These side tubes might be bare, or have ns attached, or might be enclosed in silicon carbide or similar slag resisting blocks.

It is rfurther anticipated that the side wall tube system of the boiler, indicated at I5 in Fig. 1, as well as the front and back water-wall systems, designated at 15a and 15b, shall be connected in the circulatory system and their connection may be accomplished in any suitable manner.

vIn Fig. 1, the header l2'is shown to beY partially enclosed within the lower; portion ofY the section 'l of the back wall, and the tubes I0 of the hearth extend across the top of the ash chamber between the wall sections 1 and B. .At this location, alternate tubes of the hearth are downwardly offset, as is the part Illa?, to provide spaces between the tubes through which the ash and other non-combustible materials will be discharged from the lower end ofthe hearth into the ash chamber.

As one alternative construction for the lower end portion of the hearth, it is shown in Fig. 2 that a header I 2a is disposed at the forward side of the wall 8 and the hearth tubes I0 are curved downwardly and forwardly through the wall to connect with the header, leaving the entrance to the ash pit 9 open.

Cil

Another alternative design has been illustrated in Fig. 3 wherein the hearth tubes are shown to be curved downwardly and forwardly through the wall 8 to connect with the header l2f located forwardly of the wall as in Fig.' 2, and showing also a back wall 1c that is water cooled by usev of water tubes l5d connected at their lower ends with a header I2rc which is connected in the boiler system,rand which is located at the back side of wall `L In this design, entrance to the ash pit is open.

In each of these alternative designs, the ash and non-combustibles are discharged from lthe toe of the fuel bed directly into the ash pit. lSlag at the discharge end of the hearth is apt to ad here to the exposed fire clay refractories at this location, therefore, it is desirable that this portion of the hearth be protected with a suitable facing material, such as for example, blocks vof silicon carbide, known in trade as Bernitz blocks or blocks of chrome, cast iron blocks or other material thatY has proper strength, high thermal conductivity and resistance to clinker adhesion.

Such a facing material has been indicated in Figs. 2 and 3Vby reference numeral I8 and it is shown to be applied to the hearth tubes and also to wall surfaces of the ash pit to prevent the adherence of slag thereto. In addition,y protection against slagging may be obtained by Vwelding metal strips or fins to the facing.

It is shown in Fig. 1 that the wall section 1a.' is joined with the wall section 1 by a horizontal ledge 1a, formed with a rounded nose 'Ib facing the hearth. This nose defines the top surface or a rather narrow passageL I6 between it and the hearth through which the toe of the fuel bed advances for discharge of ash and non-combustibles to the ash chamber.

Above and across the upper end portion of the hearth isY the furnace arch structure 20. This is provided with an opening 2| for the feeding of fuel to the furnace from a fuel storage bin 22. Extending across the arch structure, back of lopening 2l, is a duct 23 from which pre-heated, over-nre air is supplied under pressure to jets 24 leading downwardly and opening through the arm into the furnace. Y

Located directly below the hearth H, is a series of plenum chambers 25 from which preheated air is supplied, under pressure and in regulated amounts, to the different zones of the hearth as defined by the limits of the individual chambers.

In the present instance there are four plenum chambers, `each of which extends to the full width of the hearth. The succession of plenum chambers reaches 'from thefwall section vI to near the upper end of the hearth. Each chamberz 5. isf-supplied withlpr'e-heated air under'pressur from a suitable source of supply, here-illustrated asia duct "28,v through individual connections 29, each of which connection is equippedV with a Valve or gate .30,"whereby the amount of air admitted to the chamber may be regulated and thev pressure'of air in the chamber controlled.

Eachfplenum chamber 25 has a cross-sectional form like that of aA Veshaped trough or hopper as seen-in 'Fig 5, andisfopenat the top to the under-side of the hearth, thus providing lthat air will be supplied equally to all parts of the hearth zone and that siftings passing through thev air passages between thetubes I will be collected in the lower portion of the hopper and` may be raked outthrough the cleanouts therein designated at.32.A n. Y l

In the present preferred setting of the'hearth, in a furnace using wood rwaste fuel, its-slope is betweene and 421/2.`y The degree `of slope, however, is determined in accordance with the angle of repose of the particular fuel being used on the grate under burning conditions, and would vary with different fuels. Therefore, it is Ynot intended that the slope be limited to this range of degrees. The tubes I0 used in the hearth have an outside diameter of 31/4 inches and are so setas to provide open passages 35 about 1/8 inch wide'v between them. These passages 35 constitute about 2.6% of .the total hearth area. This should'not exceed5%.

The wood-Waste,A in its delivery downwardly 9 and the bed advances accordingly. The burning of the bed is progressive, since the present mannerl of feeding the fuel to the hearth avoids the covering of the incandescent material with green fuel. The rate of burning along the fuel bed is regulated and the proper conditions for combustion effected by the controlled rate of feeding of fuel to the hearth and the application of pre-heated forced-draft air to the individual plenum chambers and its injection through the graterpassages and fuel bed to the combustion chamber. y

It is desirable in some instances that the upper zone of the hearth be left uncoveredby the fuel bed to more or less extent in Vorder that preheated 'over-ire air may `be supplied from the corresponding plenum chamber to supplement that supplied through the otheroverdraft air supply jets. y i l v To insure complete and maximum burning rate of fuel at the toe of the yfuel bed, I provide air jets 4B extended through the wall vsection 8 and directed upwardly into the top portion of` thereon..

" 1"I'lie'f-fuel bini! contains, at the bottom thereof, one or more parallel fuel feed chain belts 50, operating 'about sprocket wheels 5i' and 52v on driven Icross shafts '53 and 54. .These belts deliver fuel from the bottom of the supply bin into a hopper 56 that discharges directly into Vthe opening 2 I y through an "air tight connection. Hingedly suspended in the hopper outlet isa gate'y 51, fixed toV a horizontal hinge shaft 58. The shaft V58 is rotatably 'mounted and a Weighted lever arm 59`is so fixedr thereto as to normally retain the. gateinr av position closing' the hopper outlet butpermitting the gate to'swing downwardly to an open position under Weight of fuel delivered thereagainst. This normally closed gateprevents furnace gasses passing 'out through the passage 2| and also is a safeguard against blowfback. v f The feeding of fuel by this means K thevalvecontrolled passage prevents any-un'- desirable -syphoning of cold air throughthe p-assage and eliminates the intaking of thefuel charge.

In Fig. 9J I have illustrated a-hearth furnac embodying' the previously Adescribed "features of thepresent invention therein, fand showing an alternative fuel feeding mechanism. In -this design, the hearth, designated b=y reference charaoter H', is substantially like that previously described in that it comprises a rbank of water tubes Ilia, connected at lupper and lower? ends' to'headers l la and 12a which, in turn, 1are' suit-v ablyconnected in the boiler circulatory system asrwas previously explained. In Vthis furnace, the arrangement of plenum chambers, and the control and'delivery of pre-heated, forced-draft air thereto is'by Ymeansl substantially like that already described. Therefore, these parts have been given reference numbers corresponding to thoseap'plied to like parts in Fig. l. shownf in Figi 9 forfeeding the fuelto the furnace will be now described.

'The furnace ychamber designated by numeral 6|) is enclosed by a back wall 6I, front wall 62 and side walls E3. The hearth H and a sloping section 6|" of theback wall of the furnace converge Y,downwardly to an ash trough 65. The hearthV tubes connect to the header l2a in the manner like that of Fig. 2 previously described. Overlying the upper end portion of the hearth and extending lforwardly from the Wall 62 as a shelf is' a furnace arch structure 68. Formed through this structure is a fuelfeed inlet 68 to which fuel may be supplied by any suitable means, preferably, byY means like or of the character of that disclosed in Fig. 1. l y

Mounted adjacent the fuel inlet, is a guide bearing 'll in vwhich a ram or plunger 12 is reciprocally contained. The ram is operable by means of a pitman rod 13,connected eccentrically to a driven wheel 14, to push the fuel, as fed through the inlet onto the upper end of the cold air with hearth, downwardlyalong the hearth for burn-f ing. The slope of the hearth is slightly lessvthan the angle of repose of the fuel that is to be burned In this design,V vover-fire yairV is admitted through jets l5 opening into the furnace through the arch structure 66.v 'I'he ducts 15 lead fromy a header- 18 andthis may be supplied With-preheated air from any suitableV source of supply. Also, air jets enter the ash pit beyond the lower end of the hearth to supply pre-heated air to` insure maximum burning-of the toe portion and through The means k 7 of the fuel bed before it is discharged into the ash pit. Y

In the furnaceof Fig. 9 I have indicated use of auxiliary fuel by the showing of oil burners 90. These are directed into the combustion chamber through openings 9! in the back Wall El. Gas or powdered coal might likewise be employed as supplemental or auxiliary fuel.

It is to be understood that a similar use rof auxiliary fuel might be made in the fulliaoe of Fig, l. In any such use of auxiliary fuel, the burners are applied in the central portion oi the combustion chamber yin order that the products of combustion vfrom the wood refuse will be compelled to pass through the zone of high temperature and turbulence, insuring complete combustion of all gases.

In a furnace where either oil, gas or powdered coal is used as auxiliary to wood waste fuel, the maximum furnace temperature is obtained by having the wood Waste fuel Subject to the radiant heat lIrorn lthe combustion of the -auxiliary fuel as will be the case in the furnace of Fig. 9, In cases where the auxiliary rfuel is a very minor portion, or where operation for extended periods will be Without the aid of auxiliary or supplement fuel, then it is proposed to have a large portion of the hearth under a refractoried arch which will reflect heat on the fuel bed, Furthermore. there should be nothing to prevent the fuel bed being subjected to maximum, radiant heat from the flame as it occurs inthe combustion chamber. Such a furnace arrangement has been illustrated in Fig, l wherein the hearth H2 is shown to extend at its lower end Linder the. overl-,ranging refractoriecl arch Structure 8,2. Where the fuel contains high percentage of moisture, it becomes necessary to have refractory walls on the sides and back of the combustion chamber in the intermediate proximity of the hearth to further reflect heat on the fuel bed for the purpose of driving off the moisture and distillng the volatiles. Such a refractioned area is designated in the triangle 85 in Fie. 1

As an alternative hearth construction, it is L..

anticipated inlieu of the close spacing of tubes lll. as shown in Fig. 6, that they be spaced farther apart and the intervening spaces be blocked ol by lugs 99 rwelded to the side walls of .adjacent tubes, as shown in Fig. '7 wherein the lugs of adjacent tubes are aligned. Another arrangelrllltrof lugs 99 isthat shown in Fig. 8 wherein those on adjacent tubes are staggered and overlapped, The area ofv air passages thus provided should not, in any arrangement, exceed of the hearth area in order toV insure necessary restriction to air flow.

In Fig-v lZ I have shown another 4modification of furnace construction embodying novel features of the presentV invention. In this, the sloping water-cooled hearth, designated at H3, is shown to'lbe connected at upper and lower ends in the boiler Ycirculation through the mediacy of headersV l lc and I2c.V The hearth area is divided into a succession of zones of control by the plenum chambers in the manner previously'described. Opposite the hearth is an inclined, water-cooled wall, I l0, and above the higher end of the hearth is a refractoried arch construction H5 whereby heat is causedto be reflected Ato effect moisture evaporation from the entering fuel. Fuel is admitted through opening H8 and ashes are discharged into pitlZ. Side walls of the furnace are here. protected against slag adhesion by Side wall tubes |25 connected at their ends in the boiler circulation. 'Auxiliary fuel burners are indicated at |30.

VAssuming that a furnace'has the novel fea-,- tures of construction of the present invention embodied therein and that the rate of feeding of fuel into the furnace is regulated in such manner as to maintain a fuel bed of proper depth and desired extent alone the hearth, and the preheated air is being supplied under pressure to the various plenum chambers and jets as required for best burning efficiency. the following conditions and advantages will be obtained.

First, a large area of fuel will be exposed to the iurnace temperature. The manner of feeding the fuel to the hearth will prevent the green fuel from covering thefuel previously fed. Injected air will cause the fuel bed to move gradually downward from a Yzone of distillation to a zone in which only the xed carbon remains. Complete burning is insured by injecting air at the toe o1 the fuel bed. Ash and non-combustible material will be discharged into the ash chamber where slag adherence is prevented by use of proper wall lining.

By reason of controlled admittance of preheated, forced-draft air to the individual plenum chambers, a zone control can be established'as may be required to best suit the fuel being used and the depth of fuel bed at the various zones. Zone control makes possible the forcing of preheated air in regulated yamounts and. pressures through the green fuel to Idrive off moisture yand volatiles. Additional air can be so injected in regulated amount and pressure through the Zone of incandescent carbon that a mixture of carbon monoxide and carbon dioxide is formed; .the former being converted into carbon dioxide in the presence of the'pre-heated, over-.draft air admitted through the various'jets or through the partly uncovered hearth at the uppermost zone.

The manner of feeding the iuel to the hearth prevents entrance of air with the fuel or the syphoning or injecting of cold air into the furnace through the feed opening. By incorporating the tubes of the hearth in the boiler circulatory system the heat that is yabsorbed by them, either from the preheated air or from the fuel, is usefully employed in the evaporation of the boiler water.

Limiting the air openings or passages through the inclined hearth to less than V5% of the hearth area and the provision of zoned air supply for the controlled application of pre-heated air to the dilferent parts of the fuel bed decreases furnace upkeep and improves the rate of burning.

The water cooled gratos generally in use, limit the temperature to which the cooling medium can be raised. YIt must be kept below the temperature of atmospheric boiling and unless distilled water is used, must be kept below the temperature at which scale forming matter will deposit, in order to avoid formation of scale within the grate. The present system, characterized by the connecting of. the water-tubes of the slopine hearth as anextension ofthe water-wall surfacein the boiler circulatory system, not only permits the cooling of the hearth by water at higher temperatures but also effects such cooling at a constant temperature corresponding to the steam temperature of the boiler. It also supplies all heat .taken from the fuel to the boiler at higher temperature range where it can be gainfully employed. o

Having thus described, my invention, what I hearth as it burns, archs overlying the upper and being parallel and extended in the direction of v slope of the hearth and closely spaced'to providev restricted air passages between them, Vmeans con-4 necting .the tubes of Vthe hearth with the circulatory system for flow of boiler watery there-` through, the lower end' portionsv of alternate water-tubes being oiset to provide spaces therebetween, an ash pit below and under the lower end of said hearth, means for injecting a controlled amount of air into said ash pit below the lowest level of said hearth for movementof air upwardly through the' ash discharging through the spaces in the end of said hearth, means at the under side of the hearth dividing the hearth area into a succession of individual zones of control and means. for supplying air under pressure and in regulated amounts to the individual zones for injection into the furnace through the restricted passages.

21A furnace and boiler combination as recited in claim 1 wherein the intertube air passages are uniformly distributed over the hearth area and comprise less than iive percent of the .total fuel bed area of the hearth. y y

3. In a furnace and boiler combination; a water-cooled hearth comprising a sloping bank of bare tubes connected in the boiler circulatory system for flow of boiler water therethrough; said tubes being extended in the direction of slope and spaced to provide restricted air passages between them, means at the higher end of the hearthY for the supplying of fuel thereonto to maintain :a fuel bed of predetermined depth lthat is caused to progress downwardly along the lower ends of said hearth respectively, air nozzle means for supplying overire air through each of said arches in a downward direction toward the bed of fuel maintained at the end portions e of said hearth, a succession of plenum chambers arranged along the hearth at its under side, and open thereto, and dividing the hearth area into asuccession of individualzones of control, a source of supply of pre-heated air, and means for effecting a controlled admittance ofA preheated air from said source of supply to each of the individual Achambers for flow therefrom to the furnace through the hearth passages and fuel bed overlying the chamber.

, 4. A furnace and-boiler combination as recited in claim 3 designed forA the burning of moist hogged fuel, and wherein the hearth is sloped at an angle within a range of 40 -to 421A?" relative to h a horizontal plane.

HENRY W. BEECHE'R.

References cited-1n theme of this patent UNITED sTATEs PATENTS Sweden June 23, 1941 

